Long-term study of physicochemical stability, microbial contamination, and endotoxin levels in UVC-photoreactor sterilized graphene-based materials

The stability of UVC-Photoreactor sterilized nanographene oxide (GOn) and partially reduced nanographene oxide (p-rGOn) was evaluated over a 12-month (M) period, when stored at room temperature (RT), 4 °C, and −20 °C. The photoreactor used, was for the first time reported for GBM sterilization. GOn and p-rGOn dispersions stored at 4 °C and −20 °C remained sterile throughout the 12 M. In contrast, dispersions of both materials stored at RT showed bacterial, fungal, and endotoxin contamination after 12 M. GOn water dispersions remained visually stable for 12 M in all storage conditions. However, the water stability of p-rGOn kept at RT was visually decreased after 8 M, when stored at 4 °C it decreased after 12 M, while at −20 °C no changes were observed. Importantly, materials stored at −20 °C could be defrosted and redispersed using bath ultrasonication (30 min), keeping their original properties and sterility. Both materials maintained consistent lateral dimensions (100–130 nm) and stable physicochemical characteristics across all storage conditions for the entire duration. This study presents, for the first time a systematic 12 M evaluation of sterile GBM stability, offering valuable insights into long-term storage strategies relevant for commercialization, transportation, and sterility assurance in biomedical-grade applications and other sensitive uses.